Method and apparatus for centrifuging fluid mixtures and selectively removing liquid material therefrom

ABSTRACT

A fluid mixture is received in a basket and rotated at high speed to form centrifugally separated inner and outer masses of material. Planing surface means is supported within the basket in normally spaced relation to the said inner mass of material. An actuating device forces the planing surface means radially outwardly against the resistance to displacement of the inner mass of material as it revolves. The actuating device is controlled to move the planing surface means radially outwardly under a substantially constant pressure which may be regulated to differentiate between resistance to displacement of the outer mass and resistance to displacement of the inner mass. The extent of travel of the planing surface means may, by means of the regulated pressure, be limited to the boundary region or interface occurring between the inner and outer masses of material. A fluid skimming tube has its tip adjustably supported in the planing surface means in slightly recessed relation such that the fluid portion of the inner mass is progressively removed as the planing surface means is travelled outwardly. When the planing surface means finds the outer mass of centrifuged material, outward travel stops and no further removal of material takes place. Pressure changes occurring when removal of material stops are utilized to control return of the planing surface means to a starting position.

United States Patent I Tholl METHOD AND APPARATUS FOR CENTRIFUGING FLUID MIXTURES AND SELECTIVELY REMOVING LIQUID MATERIAL THEREFROM David M. Tholl, Cumberland, RI.

Assignee: The De Iaval Separator Company,

Poughkeepsie, N.Y.

Filed: Jan. 28, 1971 Appl. No.: 110,391

Related US. Application Data Continuation-impart of Ser. Nos. 856,786, Sept. 10, 1969, abandoned, and Ser. No. 63,439, Aug. l3, 1970, abandoned, which is a continuation-in-part of Ser. No. 856,786.

Inventor:

U.S. Cl ..233/19 A, 233/22, 210/86 Int. Cl. ..B04b 11/00 Field of Search ..233/19 R, 19 A, 46; 2lO/86,

References Cited UNITED STATES PATENTS 450,131 7/ I936 Great Britain ..233/46 Primary Examiner-Jordan Franklin Assistant Examiner--George H. Krizmanich Attorney-Davis, Hoxie, Faithfull & Hapgood [s11 ABSTRACT A fluid mixture is received in a basket and rotated at .high speed to form centrifugally separated inner and outer masses of material. Planing surface means is supported within the basket in normally spaced relation to the said inner mass of material. An actuating device forces the planing surface means radially outwardly against the resistance to displacement of the inner mass of material as it revolves. The actuating device is controlled to move the planing surface means radially outwardly under a substantially constant pressure which may be regulated to differentiate between resistance to displacement of the outer mass and resistance to displacement of the inner mass. The extent of travel of the planing surface means may, by means of the regulated pressure, be limited to the boundary region or interface occurring between the inner and outer masses of material. A fluid skimming tube has its tip adjustably supported in the planing surface means in slightly recessed relation such that the fluid portion of the inner mass is progressively removed as the planing surface means is travelled outwardly. When the planing surface means finds the outer mass of centrifuged material, outward travel stops and no further removal of material takes place. Pressure changes occurring when removal of material stops are utilized to control return of the planing surface means to a starting position.

II III JITIII 1 PATENTED NOV 2 8 I972 SHEET UlllF 10 lzwenioay %W /M PATENTEDuuvze 1972 3.703.333

' SHEET U3UF 10 PATENTED nuv 28 I972 SHEET 07 0F 10 id M. T0 2 23, 6;; 2 4 WM PATENTEDuuv 28 I972 SHEET 100F1O Dania M1130 uitioflneag METHOD AND APPARATUS FOR CENTRIFUGING FLUID MIXTURES AND SELECTIVELY REMOVING LIQUID MATERIAL THEREFROM CROSS-REFERENCES TO RELATED APPLICATIONS The present invention is a continuation-in-part of application Ser. No. 856,786 filed Sept. 10, 1969, now abandoned, and Ser. No. 63,439 filed Aug. 13, 1970, now abandoned, which is a continuation-in-part of said application Ser. No. 856,786.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to centrifugal processing .of materials and, more particularly, to a method and apparatus for handling a fluid mixture in a rotating basket by means of which method the fluid mixture may be centrifugally separated into inner and outer masses of material and the inner mass of material may be selectively removed with the outer mass remaining substantially undisturbed. The invention is especially concerned with centrifuging certain classes of mixtures consisting of a mixture of liquid and solid components which when separated in the manner described tend to form an inner liquid layer and an outer relatively hard cake of solid material.

2. Description of the Prior Art Centrifugals of the general type referred to for handling fluid mixtures are described in U.S. Pat. Nos. 2,889,930 and 2,932,401. In these centrifugals there is provided a stationary enclosure body or curb having a basket mounted for rotation in spaced relation to the curb to carry out a desired separation of liquid from the mixture. The basket may be of the perforated type or may be of the imperforate type referred to as a clarifier. Power driving means of several different forms are employed to drive the basket through a range of centrifuging speeds. It has also been proposed to combine withcentrifugals sludge discharge means as disclosed in U.S. Pat. No. 3,407,999.

LIMITATIONS IN USE OF PRIOR ART MACHINES In separating a mixture .of the class which forms a hard outer cake on the inner surface of a centrifugal basket, it will be understood that most of the liquid component is removed through the top of the basket, but there very often will remain small amounts of liquid which are difficult to remove quickly and efficiently. This is true when using an imperforate basket especially, and even if a perforate basket is used, the perforations tend to become rather quickly clogged by a hard cake and removal of liquid is then very slow.

It will also be appreciated that with varying classes of mixtures of the type which form caked layers on the basket, the thickness of the layer may vary substantially all the way from a thin film up to a layer of from I to 5 inches in thickness or more. Although skimming devices have been proposed for removing liquid components from a rotating basket, as described, for example, in U.S. Pat. No. 3,407,999, these devices are designed to remove all of the material in the form of sludge from the basket and are not suitable for selectively removing liquid without taking away sludge or other solid material occurring as an outer mass, and as far as it is known, there is not available a skimming apparatus which is capable of moving constantly outward in a basket and removing liquid until it finds a layer of solid material whereupon it stops its travel and the skimming operation is terminated.

SUMMARY OF THE INVENTION It isa chief object of the invention to improve centrifuging methods of the type referred to and to devise a centrifugal skimming apparatus for selectively removing liquid material from a centrifugal basket, particularly small quantities of liquid which remain inside an outer annular cake of centrifuged solid material.

Another object of the invention is to devise a method of removing liquid material from a fluid mixture in which method substantially all of an inner layer of liquid material may be removed without picking up any appreciable amounts of solid material which collect as a caked layer.

Another object of the invention is to devise an improved centrifugal skimmer apparatus having a sensing shoe device for sensing the presence of a caked layer of solid material in a centrifugal basket and thereafter controlling operation of the skimmer apparatus in accordance with the physical properties of the caked layer.

Still another object of the invention is to devise a pressure actuated skimming method which is capable of sensing changes in viscosity in a fluid material and selectively carrying out the removal of fluid material in accordance with the viscosity changes sensed.

And still another object of the invention is to provide means for returning the planing surface means to a starting position immediately after removal of fluid material is terminated.

The nature of the invention andits other objects and novel features will be more fully understood and appreciated from the following description of the invention shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of a centrifugal of well-known character with which is provided a basket of the imperforate type having the skimmer apparatus of the invention combined therewith.

FIG. 2 is a vertical cross sectional view taken centrally of the machine shown in FIG. 1 and further illustrating portions of the skimmer apparatus in elevation in one position of adjustment relative to the basket.

FIG. 3 is a diagrammatic view further illustrating the centrifugal skimmer apparatus of the invention shown in a position to move into contact with centrifuged material in one section of the basket.

FIG. 4 is a detail fragmentary view further illustrating the skimming device in contact with an inner layer of centrifuged material with material being removed from this layer.

FIG. 5 is a diagrammatic view illustrating the skimmer moving into contact with an outer layer of centrifuged material at which point further travel of the skimmer outwardly is arrested.

FIG. 7 is a sectional view of the basket and centrifuged layers similar to FIG. 6 and showing the skimmer in a position in which most of the inner. layer has been removed and contact is about to be made with the outer layer. v

FIG. 8 is a view similar to FIGS. 6 7 with the skimming apparatus in a retracted position after removal of the inner layer has been completed.

FIG. 9 is a detail cross sectional view taken centrally of the skimming apparatus shown in FIG. 10.

I FIG. 10 is a detail elevational view of the skimmer apparatus illustrating planing surface means and skimmer tipin relation thereto.

FIG. 11 is a cross section taken on the line 11-1 1' of FIG. 9. v

FIG. 12 is a diagrammatic view illustrating the skimmer apparatus connected to a discharge tank.

FIG. 13 is a diagrammatic view illustrating control means operable to position the skimmer apparatus in accordance with layer change sensed by the skimmer planing means. 7

FIG. 14 is a detail elevational view of another form of skimmer tip and planing surface means.

FIG. 15 is a cross section taken on the line 15l5 of FIG. 14.

FIG. 16 is a fragmentary plan view of the skimmer and control means shown on a larger scale.

FIG. 17 is an elevational view indicating portions of the structure shown in FIG. 16 in cross section.

FIG. 18 is a diagrammatic view illustrating movement of material into and out of the centrifugal apparatus of the invention.

FIG. 19 is an elevational view partlyin cross section illustrating details of a modified form of apparatus for controlling'returnof the skimmer apparatus to astarting position. I

FIG. 20 is an elevational view of another modified means of controlling return of the skimmer apparatus to a starting position and illustrating schematically a pressure responsive device employed.

DESCRIPTION OF THE PREFERRED I EMBODIMENTS With the foregoing objectives in mind, I have conceived of an improved method of removing liquid material from ,a fluid mixture. In carrying out my improved method, the fluid mixture is received in a basket and rotated at high speeds to form centrifugally separated inner and outer masses of material. Planing surface means supported within the basket for displacement of fluid comprised by the inner mass of material is travelled outwardly under a substantially constant pressure which is controlled to differentiate between resistance to displacement of the outer mass and resistance to displacement of the inner mass, and which limits the path of travel of the planing surface means into the outer mass of material.

A fluid skimming conduit has its tip adjustably supported in the planing surface means in slightly recessed relationship such that fluid portions of the inner mass are progressively removed as the planing surface means is travelled outwardly. When the planingsurface means reaches or finds the outer mass of material, it is opposed by the relatively greater resistance to displace ment of this outer mass resulting from centrifuging.

Outward travel of the planing surface means then stops and no further removal of material through the skimmer conduit takes place.

The pressure actuated planing surface means may, I find, be employed to differentiate between resistance to displacement of the masses of centrifugally separated material of varying physical characteristics.

Thus the planing surface means may sense the difference in resistance to displacement of an inner mass of liquid as compared with the resistance to displacement of an outer mass of solids such as is constituted by a layer of caked material formed on the inside of a centrifugal basket as noted above. The planing surface means may also sense differences in resistance to displacement of two different centrifuged liquid masses of different specific gravity. Also the planing surface means may sense differences in resistance todisplacement of two centrifugally separated mixtures of liquid and solid material having different viscosities. In reference to viscosity the term viscosity as employed in the specification is intended to define any resistance to deformation that involves dissipation of energy by internal friction.

It is pointed out that the resistance of a fluid mixture of appreciable viscosity is somewhat analogous to the resistance of a thick film of lubricating'oil employed to lubricate a bearing on which a rotating journal is received. In this connection, it may be noted that the viscosity of a film of oil used in a bearing is highly important, and a helpful aid in designing bearings is the bearing characteristic number which is represented by the formula Zn/p, where Z is absolute viscosity, n is the journal speed, and p represents pressure exerted by the bearing load. I

A feature of the present invention, therefore, resides in providing planing surface means which may act somewhat as bearing surfaces when forced against centrifugally separated masses of material of varying viscosities. I

In sensing a differential in resistance by means of a surface forced under pressure into a centrifuged mass moving at speeds of from 300 rpm. up to 1,500 to 2,000 rpm. and higher, I have found that it is essential to provide for a controlled planing action in order to maintain the planing surface in a substantially stabilized state which will avoid excessive turbulence and wave action. This is particularly the case in dealing with a relatively thin layer of liquid which is required to be removed without picking up solid material. I have also found that interposing a flat or straight planing surface will fail to function properly and a satisfactory planing action can only be accomplished by means of curved planing surfaces. These curved planing surfaces preferably should have an arc of curvature which approaches somewhat close to, or may actually be, an arc of a circle.

I have still further found that it is important to combine the curved planing surface means with the skimming conduit in such a way that the conduit tip is slightly recessed with respect to the planing surface means. With this arrangement, the planing surface provides a means of entering into the stream of a centrifuged layer a limited distance depending on the surface area employed and the pressure used to force the curved surface area into the liquid. However, a further and highly important adjustment is realized by providing for advancing or retracting the tip of a conduit in the planing surface to obtain a required fine adjustment. For this purpose, I have devised a sensing shoe device having a rigid support body on which a pair of spaced curved planing surface elements may be very solidly secured in substantially parallel relationship. I have also determined that improved planing results may be obtained by forming the parallel planing surfaces with inwardly angled shapes which facilitate cutting into the centrifuged layer to be removed, while continuing to sense very small changes in resistance encountered. The inner angled planing surfaces also function in a novel manner to continuously displace liquid material inwardly and upwardly in a wave-like form which can be very precisely engaged by the recessed tip of the conduit supported between the planing surfaces described.

Considering these parts in greater detail, attention is directed to FIGS. 1 and 2 in which I have shown a typical centrifugal of the clarifier type or imperforate which includes a cylindrical curb 2 solidly mounted on a suitable base by means of suspension means 4 and partially closed at its upper side by means of a top 6; Supported within the curb 2 is an imperforate basket 8. The basket 8 is mounted for rotation within the curb 2 on a suitable shaft and bearing assembly generally indicated by the arrow 12 which is driven by a belt drive 14 from a motor driven pulley 16. A motor 20 provides a range of loading and centrifuging speeds for driving the belt and pulley arrangement described and another motor 18 may provide an independently controlled drive for the basket during a plowing operation when a plow 22 is selectively engaged by a pneumatic actuator 24 mounted at the top of the'curb to provide for scraping caked material from the basket. In accordance with the invention, I provide a pressure actuated skimmer apparatus S in combination with novel planing surface means, and portions of the skimmer apparatus are mounted externally of the curb 2 on its top portion 6 as generally shown in FIGS. 1 and 2 and also in FIGS. 16 and 17. Included in this skimmer apparatus as one important component thereof, is a skimmer conduit 30 having a tip 32. The conduit 30 is rotatably mounted in bearing means B solidly secured to the top portion 6 as shown most clearly in FIG. 17. Conduit 30 is arranged to extend downwardly into the basket 8 for a short distance into a position such as that indicated in FIG. 2. It will be observed that the vertical axis of rotation of the conduit 30 occurs in spaced relation to the central vertical axis of the basket 8 so that by rotating the conduit 30 through a short are of travel, its tip 32 may be moved toward and away from the inner periphery of the basket 8.

Rotative movement of the conduit 30 is accomplished by means of a fluid pressure actuated cylinder 34 illustrated diagrammatically in FIG. 13 and also shown in FIGS. 1, 2, l6 and 17. As noted therein, the fluid pressure actuated cylinder 34 is mounted on a bracket 35, fixed to a cylinder base 37 located above the curb top 6 as illustrated in FIG. 2. Bracket 35 and one end of cylinder 34 are pivotally supported on a swivel plate 33, as shown in FIG. 17. Pressure, for example, from a suitable source of compressed air is regulated by a pressure regulator device 36 of conventional character having a pressure gauge 45. A solenoid valve 47 located adjacent the regulator 36 and more clearly shown in FIG. 13 is operated by an electrical switch device 38 noted in FIGS. 16 and 17 and also shown schematically in FIG. 13. The switch device 38 may also be provided with a time clock control 51 (FIG. 13) for use where it may be desired to operate the solenoid switch through any desired time interval. As indicated in FIG. 13, the solenoid valve 47 controls flow of compressed air to the cylinder 34 which is a double-acting cylinder and operates under control of switch 38 to move a plunger rod 34a in one direction when one side of the valve 47 is open and to move the plunger rod 34a in an opposite direction when the solenoid valve is in a second position.

Plunger rod 344 is connected to a curved link part 55 pivotally connected to an arm 57. The arm 57 includes clevis portions adjustably fastened by a bolt 57a around the conduit member 30 as shown in FIGS. 16 and 17. The plunger rod 34a has supported at right angles thereto a bar 53 and attached to an opposite end of the bar 53 is a plunger rod 59 (FIG. 16) which forms a part of a pneumatic damping device comprising a cylinder 61 which is of a conventional adjustable air escape type. This damping device serves to cushion vibration occurring when the conduit 30 and the planing means move against fluctuating resistance in a centrifuged body of liquid which is being removed.

FIG. 12 is intended to illustrate conduit 30 extending upwardly and into a receptacle 30 for containing liquid which is removed from the basket 8 and FIG. 18 also illustrates diagrammatically travel of material from the centrifuge into containers.

As noted above, an important feature of the invention is the combination with conduit 30 of special fluid planing surface means preferably attached at either side of the lower end of the conduit 30 closely adjacent to the conduit tip 32. The planing surface means is designed to travel with conduit 30 and to move under pressure into contact with an innermost layer of centrifuged fluid in the basket 8 in opposed relationship to the path of flow of the fluid.

When thus forced against the centrifuged fluid, there is immediately set up an appreciable resistance to displacement by the centrifuged liquid and this resistance can be overcome by a suitable pressure which determines the extent to which the planing surface means enter into the fluid. The term fluid planing surface means, as employed in the specification, is intended to include any surface which may be interposed in the path of flow of centrifuged separated masses to sense changes in resistance of the masses to displacement.

In the preferred form of the invention as shown in the drawings, the fluid planing surface means may be comprised by apair of spaced apart curved planing elements 40 and'42 having flat planing surfaces 40a and 40b. These members 40 and 42 are supported at the lower end of the skimmer conduit at opposite sides of the conduit tip 32 in an angularly disposed position so that when the conduit 30 is rotated about its vertical axis, the elements 40, 42 can be moved through a short are of travel against the flow of an innermost surface of centrifugally separated masses in the basket 8. By controlling the pressure exerted through the cylinder 34, the extent towhich the planing surfaces are submerged,

as well as the tip 32, may be controlled to a considerable extent. In addition, the tip 32 of the conduit 30 may be arranged in slightly recessed relationship to the planing surfaces of the elements 40 and 42 as shown in FIGS.,9, 10 and 11 in order to provide for a controlled removal of fluid through the tip 32. It is further found that the positioning of the tip 32 under some conditions may be quite critical and should not extend into the centrifuged fluid more than about from one-sixteenth of an inch to one thirty-second of an inch.

For purposes of providing a further adjustment to meet this critical position need, I have provided at the bottom of the conduit 30, a tubular frame piece 46 which is threaded onto a similarly threaded reduced end of the conduit 30 as shown in FIG. 9. This tubular frame piece46 at its opposite end is also threaded to receive a reduced threaded end of the tip 32. By ad vancing or retracting the tip 32 in this threaded frame piece, a fine adjustment may be realized for collecting varying quantities of material from a centrifuged layer.

When using the fluid planing surface means with fluid mixtures which are centrifuged at relatively higher speeds ranging from 300 rpm. up to 1,500 to 2,000 rpm, I find that thecurvature of the planing surfaces 40a and 40b becomes quite significant and should approach very closely, or actually constitute, an'arc of 'a circle of a suitably controlled radius in order to avoid excessive turbulence and splashing and tocarry out a smooth removal operation. It is also found that preferred results may be obtained by furthervarying the planing surfaces 40a and 40b, and in FIGS..14 and 15, I have illustrated elements 40 and 42' which are formed with inwardly angled planing surfaces'40c and 420. These angled planing surfaces extend inwardly toward one another and function to cut into a rotating fluid body quite sharply with a continuous wave or flow of fluid being forced inwardly and against the recessed tip 32 in a desirable manner. At the same time, there is reduction in wave disturbance in the fluid at the outer sides of the planing surfaces. It is pointed out that these advantages are realized while still retaining in the, angled surfacesthe ability to sense changes in resistance of different masses which are contactedby the planing surfaces as they move outwardly.

The technique of differentiating by pressure actuated planing surfaces variations in resistance to displacement of two or more centrifugally separated masses is rendered appreciably more effective by certain conditions inherent in a centrifuging operation. G forces are exerted in the separated masses in varying degree dependent on the radius of rotation and these G forces tend to multiply each mass weight so that a sharper boundary or interface is present and may be more readily detected by a planing surface.

As has been described above, movement of the planing surfaces is accomplished by a regulated pressure of compressed air passed through the pressure regulator 36 during a centrifuging cycle which may, for instance, by of 4 or 5 minutes duration. In the method of the invention, the pressure is set at a suitable value which will move the surfaces outwardly at a constant rate of travel as liquid is removed through conduit 30. During this travel of the planing surfaces outwardly, it will be un-' derstood that a substantially constant pressure is exerted at all times. At a point where the planing surfaces come into contact with an outer centrifuged mass whose resistance to displacement exceeds the pressure supplied to the cylinder 34, further outward travel stops and removal of liquid is terminated. Thereafter, I may provide for controlling the planing surfaces in any one of several different ways. In some cases, where a cycle of centrifuging occurs throughout an interval of time which is substantially longer than the period required for the skimmer to remove desired amounts of liquid, the planing surfaces 40a and 42a may be allowedto plane around the inner surface of a layer of caked material until the centrifuging cycle is completed as controlled by the time switch 51. At the end of this period, the solenoid valve 47 is operated by switch 51 to reverse flow of compressed air to the cylinder 34 and the tubular conduit is then rotated to a starting posi tion.

I may also desire to return the planing surfaces to a starting position at any point where there is encountered a resistance which exceeds the pressure employed for actuating outward travel of these surfaces. For example, I may take advantage of the pressure drop which occurs in the conduit 30 at such time as removal of material from one layer is completed and no further flow of fluid is passing upwardly through the conduit to the storage tank 30'. As one means of employing this pressure drop, I may, for example, provide an arrangement such asthat illustrated diagrammatically in FIG. 12 and shown in more detail in FIG. 19. i As illustrated in FIG. 19 a pressure switch member 60 issupported externally of a conduit 300 at an upper end thereof and a pipe 64 is connected into the conduit base as shown in a position to sense change in pressure in the conduit 30a. Portions of the conduit 30 below the switch 60 are suitably supported in a bearing B of a curb 6" in. the manner earlier described. A micro switch member 38' mounted on a cylinder base 37 is operated through an electrical conductor 62 connected into the pressure switch 60 as shown.

The switch 60 may be of the diaphragm type having a pressure sensing diaphragm which communicates with one end of the pipe 64. A pressure adjustment means 72 is secured through an upper side of the switch housing 74 and may be set to control the spacing of a diaphragm regulated contact 76 relative to a pivotted switch element 78. The switch element 78 operates a circuit through the switch terminal block 80 to the main switch 38.

With a suitable setting of the diaphragm switch, a pressure drop in conduit 30a resulting from termination of flow of material therethrough will cause the switch to operate the main switch 38', and this in turn operates a solenoid such as solenoid 37, to reverse movement of a cylinder plunger and return the planing surfaces and skimmer tip to a starting position.

It will be understoodthat the above-described circuit may be arranged to by-pass the clock control circuit and, therefore, sliding contact of the planing surface means with a hard cake or layer may be stopped as desired.

It is further pointed out that using a control such as pressure switch 60 may be advantageous in cases where the thickness of a cake or layer to be left is not readily ascertainable and thus an exact centrifuging period cannot be established beforehand and an excessive use of the centrifuging apparatus may take place.

I have also found that a pressure drop in the skimmer apparatus described may be sensed at other points and employed to control movement of the skimmer tip to a starting position. For example, in FIG. I have illustrated diagrammatically a damping cylinder 90 of the type similar to the cylinder 61 in FIG. 16. A wellknown characteristic of such a damping cylinder is the controlled exhaust of air or other fluid from one end of the cylinder with a pressure being realized in the cylinderas long as a resistance is encountered by the planing surface means.

As shown in FIG. 20, a pipe 92 is arranged to communicate with the pressure region in the cylinder 90 and to sense a drop in pressure resulting from interruption in outward travel of the planing surface means. The pipe 92 may, for example, connect with a pressure switch arrangement 94 whose contacts 96, when opened by a drop in pressure, will operate a springreturn synchronous liner apparatus 98. Operation of 98 acts against a spring 100 to pivot an arm 102 and actuate electrical switch 104. Switch 104 controls a solenoid such as the solenoid 37 earlier described. Various other arrangements of this nature may be employed.

In carrying out the method of the invention, utilizing the apparatus now described, it will be understood that various classes of fluid mixtures may be processed. However, the invention is especially designed to handle fluid mixtures which when centrifuged tend to form a relatively hard outer layer or cake of material which collects around the inner peripheral surface of the basket. There are a number of mixtures of this class which frequently require separation.

As an example of one such mixture, there may be cited a mixture of zinc fines in an oily base, a product which is produced in the course of certain photo-engraving processes where considerable quantities of zinc are used and a rapid separation process is required.

In a typical centrifuging operation of the invention for removing liquid materials from zinc fines, I may, for example, employ a centrifugal having an inner diameter of 32 inches and an axial height of 20 inches, thus providing a volume of 6.7 cubic feet. Ordinarily, the basket when filled will hold a batch of approximately 50 gallons of fluid material and a typical operating speed for the basket may be approximately 50 to 100 r.p.m. With a batch of material of the type and volume indicated being centrifuged in the basket and run at speeds noted, the zinc fines are quickly forced outwardly against the inner periphery of the basket and an inner layer of liquid forms and flows upwardly and outwardly over the top of the basket. In an average case, this may require a period of from 2% to 2% minutes. At

this point, a substantial thickness of cake is formed and further removal of liquid is very slow and a thin layer of liquid remains to be removed, and for this purpose the 7 method of the invention is especially useful.

In FIGS. 3 to 9, inclusive, I have illustrated diagrammatically two centrifugally separated masses including wardly into the inner layer of liquid 50 as shown in FIGS. 4 and 6 and begin to remove small amounts of this liquid in a carefully controlled manner. After a short period, substantially all of the inner layer of liquid is removed, as suggested in FIGS. 5 and 7, and the planing surfaces gradually come into contact with the caked layer of zinc fines 52 as suggested in FIGS. 5 and 7. Under a pressure of 26 pounds per square inch, the planing surfaces meet the resistance to displacement of the cake of zinc fines 52 and this resistance, for example 28 to 30 pounds, exceeds the pressure of 26 pounds, and further outward travel of the planing surfaces stops. I

At this point, the planing surfaces may be allowed to continue to plane around the caked material during the short interval which remains in the timing cycle set by the timing clock disclosed; If the pressure switch type of operation, earlier disclosed, is desired, as soon as pressure drops in the conduit 30, the pressure switch 60 closes a circuit 62 by-passing the clock circuit and reversing the solenoid valve 47 and movement of the cylinder 34 to return the planing surfaces to a starting position. From the foregoing disclosure, it will be seen that I have provided an improved method of centrifugal separation which may be used in separating various classes of solids, liquids and mixtures of these materials and separation may be selectively carried out with respect to two or more centrifugally separated masses.

I claim:

.1. In a centrifugal apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and fluid mixture and providing centrifugally separated masses, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip located in the lower end of the skimming conduit for collecting and removing fluid material from the basket, a sensing device consisting in planing surface means mounted on the skimming conduit and movable with the conduit tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the said centrifugally separated masses, and pressure actuated means responsive to resistance sensed by the planing surface means for controlling travel of the conduit tip.

2. In a centrifugal apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and fluid mixture and providing centrifugally separated masses, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip located at the lower end of the skimming conduit for collecting fluid material, a sensing device consisting in planing surface means movable with the tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the said centrifugally separated masses, and pressure actuated means responsive to resistance sensed by the planing surface means for moving the tip in a limited arc of travel which extends through one of the centrifugally separated masses.

3. In a centrifuge apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and arranging the fluid mixture in centrifugally separated inner and outer masses, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip element located at the lower end of the conduit for collecting and removing fluid material from the basket, a sensing device consisting in planing surface means mounted on the said lower end of the conduit and movable with the conduit tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the said centrifugally separated masses, and pressure actuated means for progressively moving the tip and the planing surface means through a limited arc of travel under a constant pressure which is less than the pressure required to force the planing surface means into the said outer centrifugally separated mass.

4. In a centrifuge apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and separating the fluid into an outer layer of compacted solids and an inner layer of liquid material, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip formed at the end of the conduit, sensing means comprising planing elements arranged at either side of I the tip and movable with the conduit tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the centrifugally separated layers, and pressure actuated means responsive to resistance sensed by the planing surface means for moving the conduit tip into the inner layer liquid material under a pressure whish is less than the pressure required to force the planing surface means into the layer of compacted solids.

5. In a centrifuge apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and separating the fluid into an outer layer of compacted solids and an inner layer of liquid material, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a tip formed at the end of the conduit, pressure actuated means for moving the conduit towards the liquid layer, planing surface means arranged beside the tip and movable with the conduit into planing contact with the liquid layer to locate the tip in a position to selectively remove the liquid layer from the basket, and pressure regulating means for limiting the pressure exerted by the pressure actuated means to a value below the pressure required to force the planing surface means into the outer layer of compacted solids;

6. A structure according to claim 1 in which the conduit tip is arranged in recessed relationship to the planing surface means.

7. A structure according to claim 6 in which the conduit tip is adjustably secured in the conduit to vary the recessed relationship with the planing surface means.

8. A structure according to claim 1 in which the planing surface means includes a pair of spaced apart planing elements supported at either side of the conduit tip and formed with curved planing surfaces.

9. A structure according to claim 8 in which the curved planing surfaces extend angularly inwardly toward one another in a position to direct fluid inwardly toward the conduit tip.

10. A structure according to claim 1 in which the pressure actuated means for controlling travel of the conduit tip includes a fluid pressure operated cylinder operatively connected to the skimmer conduit, a pressure regulating valve for regulating flow of fluid under pressure to the cylinder, a solenoid valve through which fluid from the regulating valve is passed to the cylinder, and electrical switch means for opening and closing the solenoid valve.

11. A structure according to claim 10 in which the electrical switch means includes a time clock for reversing the cylinder to return the skimmer conduit to a starting position.

12. A structure according to claim 11 in which the skimmer conduit is provided with a pressure sensing switch for returning the conduit to a starting position when the removal of liquid material through the conduit ceases.

13. In a method of centrifuging a fluid mixture in which the fluid mixture is processed in a rotating basket to provide centrifugally separated masses of material, and a skimmer conduit tip is introduced into the centrifuged mixture to selectively remove fluid material, the steps which include supporting on the skimmer conduit planing surface means for sensing differences in resistance to liquid displacement in the centrifugally separated masses, advancing both the conduit tip and the planing surface means along an arcuate path of travel into the centrifuged mass to progressively remove fluid material, and controlling the removal of fluid material in response to changes in resistance sensed by the planing surface means as it moves along said arcuate path.

14. A method according to claim 13 in which the fluid mixture is centrifugally separated into an inner liquid mass and an outer solid mass, and removal of material is terminated when resistance to fluid displacement of the solid mass is sensed by the planing surface means.

15. A method according to claim 13 in which the fluid mixture is centrifugally separated into an inner liquid mass and an outer liquid mass and removal of material is terminated when resistance to fluid displacement of the outer liquid mass is sensed by the planing surface means.

16. A method according to claim 13 in which the fluid mixture is centrifugally separated into an inner mass of relatively low viscosity and an outer mass of relatively high viscosity, and removal of material is terminated when resistance to displacement of the outer mass is sensed by the planing surface means.

17. A method of separating materials which includes containing a fluid mixture of the materials in a rotating basket, centrifugally displacing the materials outwardly to provide separated masses of varying resistance to displacement, supporting in the basket a skimmer conduit tip and a device for sensing resistance to fluid displacement in the separated masses, progressively moving both the sensing device and the conduit tip along an arcuate path against the resistance of portions of the fluid mixture to remove material through the skimmer conduit, and limiting the extent of the arcuate path of travel in accordance with the resistance to fluid displacement sensed by the planing surface means.

18. A method according to claim 17 in which the skimmer conduit and the planing surface means are moved by a pressure actuated device and the pressure actuated device is operated to return the skimmer conduit to a starting position after removal of material is completed.

19. A method of separating materials which includes containing a mixture of liquid and solid material in a rotating basket, centrifugally displacing solid material outwardly to provide fluid mixture portions whose viscosity increases in a direction radially outwardly, supporting a skimmer conduit in a device for sensing resistance of the fluid mixture, progressively moving the sensing device outwardly against the resistance of portions of the fluid mixture of increasing viscosity to remove material through the skimmer conduit andthen interrupting movement of the sensing device at a predetermined point which is controlled by the increasing viscosity of the fluid mixture to limit the amount of material removed through the conduit.

20. A structure according to claim 1 in which the tubular skimming conduit includes a pressure sensing switch arranged to sense a drop in pressure when flow of fluid through the conduit is stopped, and means responsive to the pressure sensing switch for returning the skimmer tip and planing surface means to a starting position.

21. A structure according to claim 1 in which the tubular skimming conduit includes a pressure sensing switch arranged to sense a drop in pressure when flow of fluid through the conduit is stopped, and means responsive to the pressure sensing switch for returning the skimmer tip and planing surface means to a starting position, and a pressure sensing means connected into the conduit for sensing a drop in pressure and operating the said electrical switch.

22. A structure according to claim I in which the pressure actuated means for controlling travel of the conduit tip includes a fluid pressure operated cylinder operatively connected to the skimmer conduit, a pressure regulating valve for regulating flow of fluid under pressure to the cylinder, a solenoid valve through which fluid from the regulating valve is passed to the cylinder, and electrical switch means for opening and closing the solenoid valve, and said pressure operated cylinder including a damping cylinder for exhausting fluid under pressure. 

1. In a centrifugal apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and fluid mixture and providing centrifugally separated masses, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip located in the lower end of the skimming conduit for collecting and removing fluid material from the basket, a sensing device consisting in planing surface means mounted on the skimming conduit and movable with the conduit tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the said centrifugally separated masses, and pressure actuated means responsive to resistance sensed by the planing surface means for controlling travel of the conduit tip.
 2. In a centrifugal apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and fluid mixture and providing centrifugally separated masses, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip located at the lower end of the skimming conduit for collecting fluid material, a sensing device consisting in planing surface means movable with the tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the said centrifugally separated masses, and pressure actuated means responsive to resistance sensed by the planing surface means for moving the tip in a limited arc of travel which extends through one of the centrifugally separated masses.
 3. In a centrifuge apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and arranging the fluiD mixture in centrifugally separated inner and outer masses, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip element located at the lower end of the conduit for collecting and removing fluid material from the basket, a sensing device consisting in planing surface means mounted on the said lower end of the conduit and movable with the conduit tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the said centrifugally separated masses, and pressure actuated means for progressively moving the tip and the planing surface means through a limited arc of travel under a constant pressure which is less than the pressure required to force the planing surface means into the said outer centrifugally separated mass.
 4. In a centrifuge apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and separating the fluid into an outer layer of compacted solids and an inner layer of liquid material, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a conduit tip formed at the end of the conduit, sensing means comprising planing elements arranged at either side of the tip and movable with the conduit tip into planing contact with the centrifuged mixture for sensing differences in resistance to fluid displacement of the centrifugally separated layers, and pressure actuated means responsive to resistance sensed by the planing surface means for moving the conduit tip into the inner layer liquid material under a pressure whish is less than the pressure required to force the planing surface means into the layer of compacted solids.
 5. In a centrifuge apparatus of the class which includes a curb having a basket rotatably mounted therein for receiving a fluid mixture and power driving means for rotating the basket and separating the fluid into an outer layer of compacted solids and an inner layer of liquid material, the combination of a tubular skimming conduit rotatably supported on the curb in a position to extend downwardly into the basket, a tip formed at the end of the conduit, pressure actuated means for moving the conduit towards the liquid layer, planing surface means arranged beside the tip and movable with the conduit into planing contact with the liquid layer to locate the tip in a position to selectively remove the liquid layer from the basket, and pressure regulating means for limiting the pressure exerted by the pressure actuated means to a value below the pressure required to force the planing surface means into the outer layer of compacted solids.
 6. A structure according to claim 1 in which the conduit tip is arranged in recessed relationship to the planing surface means.
 7. A structure according to claim 6 in which the conduit tip is adjustably secured in the conduit to vary the recessed relationship with the planing surface means.
 8. A structure according to claim 1 in which the planing surface means includes a pair of spaced apart planing elements supported at either side of the conduit tip and formed with curved planing surfaces.
 9. A structure according to claim 8 in which the curved planing surfaces extend angularly inwardly toward one another in a position to direct fluid inwardly toward the conduit tip.
 10. A structure according to claim 1 in which the pressure actuated means for controlling travel of the conduit tip includes a fluid pressure operated cylinder operatively connected to the skimmer conduit, a pressure regulating valve for regulating flow of fluid under pressure to the cylinder, a solenoid valve through which fluid from the regulating valve is passed to the cylinder, and electrical switch means for opening and closing the solenoid valve.
 11. A structure according to claim 10 in which the electrical switch Means includes a time clock for reversing the cylinder to return the skimmer conduit to a starting position.
 12. A structure according to claim 11 in which the skimmer conduit is provided with a pressure sensing switch for returning the conduit to a starting position when the removal of liquid material through the conduit ceases.
 13. In a method of centrifuging a fluid mixture in which the fluid mixture is processed in a rotating basket to provide centrifugally separated masses of material, and a skimmer conduit tip is introduced into the centrifuged mixture to selectively remove fluid material, the steps which include supporting on the skimmer conduit planing surface means for sensing differences in resistance to liquid displacement in the centrifugally separated masses, advancing both the conduit tip and the planing surface means along an arcuate path of travel into the centrifuged mass to progressively remove fluid material, and controlling the removal of fluid material in response to changes in resistance sensed by the planing surface means as it moves along said arcuate path.
 14. A method according to claim 13 in which the fluid mixture is centrifugally separated into an inner liquid mass and an outer solid mass, and removal of material is terminated when resistance to fluid displacement of the solid mass is sensed by the planing surface means.
 15. A method according to claim 13 in which the fluid mixture is centrifugally separated into an inner liquid mass and an outer liquid mass and removal of material is terminated when resistance to fluid displacement of the outer liquid mass is sensed by the planing surface means.
 16. A method according to claim 13 in which the fluid mixture is centrifugally separated into an inner mass of relatively low viscosity and an outer mass of relatively high viscosity, and removal of material is terminated when resistance to displacement of the outer mass is sensed by the planing surface means.
 17. A method of separating materials which includes containing a fluid mixture of the materials in a rotating basket, centrifugally displacing the materials outwardly to provide separated masses of varying resistance to displacement, supporting in the basket a skimmer conduit tip and a device for sensing resistance to fluid displacement in the separated masses, progressively moving both the sensing device and the conduit tip along an arcuate path against the resistance of portions of the fluid mixture to remove material through the skimmer conduit, and limiting the extent of the arcuate path of travel in accordance with the resistance to fluid displacement sensed by the planing surface means.
 18. A method according to claim 17 in which the skimmer conduit and the planing surface means are moved by a pressure actuated device and the pressure actuated device is operated to return the skimmer conduit to a starting position after removal of material is completed.
 19. A method of separating materials which includes containing a mixture of liquid and solid material in a rotating basket, centrifugally displacing solid material outwardly to provide fluid mixture portions whose viscosity increases in a direction radially outwardly, supporting a skimmer conduit in a device for sensing resistance of the fluid mixture, progressively moving the sensing device outwardly against the resistance of portions of the fluid mixture of increasing viscosity to remove material through the skimmer conduit and then interrupting movement of the sensing device at a predetermined point which is controlled by the increasing viscosity of the fluid mixture to limit the amount of material removed through the conduit.
 20. A structure according to claim 1 in which the tubular skimming conduit includes a pressure sensing switch arranged to sense a drop in pressure when flow of fluid through the conduit is stopped, and means responsive to the pressure sensing switch for returning the skimmer tip and planing surface means to a starting position.
 21. A struCture according to claim 1 in which the tubular skimming conduit includes a pressure sensing switch arranged to sense a drop in pressure when flow of fluid through the conduit is stopped, and means responsive to the pressure sensing switch for returning the skimmer tip and planing surface means to a starting position, and a pressure sensing means connected into the conduit for sensing a drop in pressure and operating the said electrical switch.
 22. A structure according to claim 1 in which the pressure actuated means for controlling travel of the conduit tip includes a fluid pressure operated cylinder operatively connected to the skimmer conduit, a pressure regulating valve for regulating flow of fluid under pressure to the cylinder, a solenoid valve through which fluid from the regulating valve is passed to the cylinder, and electrical switch means for opening and closing the solenoid valve, and said pressure operated cylinder including a damping cylinder for exhausting fluid under pressure. 